Technical Field
The present invention relates to a light source device using laser light and an image projector including the light source device.
Description of Related Art
Nowadays, an image projector that projects on a screen an image using image data stored in a screen, a video image, and a memory card and so on of a personal computer is conventionally known. The image projector is configured to project the image on the screen by light emitted from a light source device by use of a micro mirror display element, a liquid crystal plate, and so on, referred to as a DMD (digital micro mirror device).
In recent years, the light source device of the image projector employs as a light source a light-emitting diode (LED), a laser diode (LD), and a semi-conductor element such as organic EL (electroluminescence) and so on.
By the way, laser light is coherent light having an aligned wave surface and great straightness. Therefore, there is possibility that, if the laser light directly enters eyes of a person, it gives an obstacle to retina. In addition, because the laser light has great energy strength, there is possibility that, when the laser light is irradiated to the skin of a person, it affects on a human body.
Therefore, there is known a technology in which a diffusion member to relieve energy density of laser light of a high output is provided on a traveling light path of the laser light such that the laser light is directly emitted to an exterior of the image projector to contribute to the improvement in safety for the laser light in the light source device of the image projector including the laser light source (see Japanese Patent Application Publication No. 2010-231063).
If the laser light of a high output continues to be irradiated to the diffusion member made of glass, the diffusion member tends to generate heat breaking and damage. In other words, because glass has a very small heat conductivity, expansion force is locally added to a heated portion only by the irradiation of the laser light. As a result, a difference in thermal stress between the heated portion and a periphery of the heated portion occurs, and the heat breaking occurs in the diffusion member when the difference in thermal stress exceeds a breaking limit of glass.
It is important not to break the diffusion member to prevent the laser light from leaking directly to an exterior of the image projector without the laser light being diffused.
However, a technology disclosed in Japanese Patent Application Publication No. 2010-231063 as described above premises that the laser light is not leaked to an exterior if the diffusion member departs from the traveling light path of the laser light. The technology does not consider a case where the diffusion member does not exist in a normal state in the travelling light path of the laser light by breaking a part of the diffusion member even if the diffusion member does not depart from the travelling light path of the laser light. Therefore, it is necessary to contemplate further improvement in safety for the laser light.